In automotive engineering, automatic transmissions, in particular stepped fully automatic transmissions with hydrodynamic torque converter and planetary transmissions are used for power transmission beside manual variable-speed transmissions.
Such fully automatic stepped transmissions act as powershift transmissions without interruption of the tractive force, wherein the power flow is effected via planetary gearsets and the gear changes occur by coupling or releasing individual planetary gearset elements. The coupling of individual planetary gearset elements presently is effected by means of multidisk clutches which must be designed for a maximum torque to be transmitted and comprise a corresponding number of friction points and disks for torque transmission. Due to the numerous friction points, the undesired drag torques are quite high in the decoupled condition and have a disadvantageous effect on the transmission efficiency.
For this reason, the generic DE 102 44 523 A1 already has proposed a vehicle transmission in which the Internal disk carrier is coupled with a rotatable transmission component, e.g. a transmission shaft, via a synchronizer. The synchronizer selectively provides for a decoupling, a frictional coupling or a positive coupling of the internal disk carrier with the transmission shaft. In the decoupled condition of the synchronizer drag torques likewise occur, which due to the considerably smaller friction surfaces as compared to the multidisk clutch however are distinctly smaller. In the decoupled condition of the shifting device, i.e. with open multidisk clutch and decoupled synchronizer, the lower drag torques result in a relative rotation exclusively or at least for the most part in the region of the synchronizer and hardly or no longer at all in the region of the multidisk clutch, so that the transmission efficiency is increased.
However, the construction of the vehicle transmission as disclosed in DE 102 44 523 A1 is relatively complex and in addition has an undesirably high shifting force level. According to FIG. 7, the high shifting force level results from the fact that the actuating body is urged into a decoupled starting position of the shifting device by a first spring means and a third spring means. To ensure the desired functionality of the shifting device, the third spring means must be designed softer than the first spring means. However, the third spring means also must be hard enough to ensure a safe design of the positive connection between the toothing profiles. These requirements of the spring means in total lead to an undesirably high shifting force level of the shifting device proposed in the prior art.
It is the object of the invention to create a constructively simple shifting device for a motor vehicle transmission, which due to low drag torques contributes to a high transmission efficiency and in addition has a low shifting force level.